Certain acyloxy thiazolidines and process for their manufacture

ABSTRACT

Process which comprises treating a saturated cyclic Alpha hydrazino-thioether, in which the hydrazino group is N,N&#39;&#39;disubstituted by esterified carboxyl groups, with an oxidation reagent capable of furnishing an acyloxy group; in a resulting saturated cyclic Alpha -acyloxy-thioether the acyloxy group may be converted into the hydroxyl group. The products are useful in the synthesis of 7-amino-cephalosporanic acids.

0 United States Patent [151 3,681,370 Woodward 1 Aug. 1, 1972 [54] CERTAIN ACYLOXY THIAZOLIDINES [58] Field of Search ..260/306.7

AND PROCESS FOR THEIR MANUFACTURE References Ci [72] Inventor: Robert Burns Woodward, 12 Oxford UNITED STATES PATENTS Cambndge Mass 02138 3,522,266 7/1970 Woodward ..260/306.7 [22] Filed: Nov. 24, 1969 Primary Examiner-Alex Mazel [21] Appl' 8796l6 Assistant Examiner-R. J. Gallagher Related 1,5, Appucation Data Attorney-Harry Goldsmith, Joseph G. Kolodny and M A. M [62} Division of Ser. No. 573,891, Aug. 22, 1966, am Pat. NO. 30 Foreign li ti P i i D t Process which comprises treating a saturated cyclic ahydrazino-thioether, in which the hydrazino group is Sept. 10, 1965 Sw tzerland ..12623/65 N,Nl disubstituted by eserified carboxyl g p with Dec. 9, Sw tzerland an oxidation reagent p bl of an y y Dec. 9, 1965 Sw tzerland ..l6972/65 group; in a resulting t t d cyclic a-acyloxy- Jan. 13, 1966 Sw tzerland ..447/66 thioether the y y g p y be converted into the Feb. 3, 1966 Switzerland "1529/66 yd g p The products are useful in the y sis of 7-amino-ce halos ranic acids. 52 us. Cl ..260/306.7 p [51] Int. Cl. ..C07d 91/16 10 Claims, No Drawings CERTAIN ACYLOXY AND PROCESS FOR MANUFACTURE CROSS-REFERENCES TO RELATED APPLICATIONS This is a divisional application of application Ser. No. 573,891, filed Aug. 22, 1966 and now US. Pat. No. 3,522,266 issued July 28, 1970.

The present invention provides a method procedure I for the manufacture of acyloxy compounds and the corresponding hydroxy derivatives, which was used in the production of valuable intermediate products and especially in the first production of synthetic 7-aminocephalosporanic acid and its derivatives, and lends itself particularly well to this peculiar senthesis.

7-Amino-cephalosporanic acid corresponds to the formula COOH 0 to the manufacture of valuable medicaments, and of its derivatives is based on the conception to use a 3,5-unsubstituted 2,2-disubstituted thiazolidine 4-carboxylic acid, for example,a compound of the formula c0011 CH-CE2 HN .r, 1110/ CH;, I

as the starting material and to carry out the novel synthesis, for example, according to the following s xvr 25 scheme of formulas:

c0011 ooorr ooocm err-om on, err-0 1 CH; (SH-0H2 HN s cm-e-o-m-n s orr,-c o o N s II l o H; o c n, c CH3 CH: CH: CH: CIT; CH3

1 II III lIf-GOOCII: rl-ooocm 3 5 000cm oooom N-NH-COOCH: on: err-cg PMOCOCH') CH; CH-CH 4 cH,-o-o c-N s CH:$O-CN/ s CH; 0 H, c

1' CH3 CH3 CH3 CH3 iv v 900cm ooocrr, 0H 5 I 1, CH; CH-cg CH: CH-CH crr=-h -o-( 3-N s CH= -o c N s n; /c on, /0\

CH3 CH: CH; CH:

ooocn, o=o nu 131112 on; GIL-CH 0m oil-oil impound: J3 oln-c o-C-N s 011;- -OCN II ll cm 0 c 113 C OH; on, Ca, crr;

IX vtrr The compounds of the formula X used as the intermediate is manufactured in the following manner:

The above mentioned compounds, which are valuable intermediates, for example the compounds of the formulas V and VI, are unexpectedly obtained when a saturated cyclic -hydrazino-thioether, in which the hydrazine group is N,N'-disubstituted by esterified carboxyl groups, for example, the compound of the formula IV, is treated with an oxidation reagent capable of furnishing an acyloxy group and, if desired, in a resulting saturated cyclic a-acyloxy-thioether the acyloxy group is converted into the hydroxyl group, and/or, if desired, in a resulting compound a substituent is converted into another, and/or if desired a resulting mixture of isomers is resolved into its component isomers.

Acyl radicals of an acyloxy group furnished by the oxidation reagent during the reaction are the acyl radicals of organic carboxylic acids, especially of aliphatic carboxylic acids, such as alkane carboxylic acids, especially lower alkane carboxylic acids, in the first place acetic acid or propionic acid, or of aromatic carboxylic acids, such as benzoic acid. These acids are unsubstituted, but may carry further substituents, such as lowe r alkyl or lower alkoxy groups or halogen atoms or pseudohalogen groups, such as trifluoromethyl groups.

Oxidation reagents capable of furnishing acyloxy groups are in the first place heavy metal acylates with oxidizing properties. Particularly suitable are lead tetraacylates and especially lead tetraacetate, as well as lead tetrapropionate, lead tetrastearate, lead tetrabenzoate, lead tetra-3-bromobenzoate, as well as thallium-lIl-acylates, such as thallium-lll-acetate, or mercury-ll-acylates, such as mercury-Il-acetate. If desired, these oxidants may be formed in situ, for example, by reacting lead dioxide or mercuric oxide with an organic carboxylic acid, such as acetic acid, and/or, if desired, used in the presence of a bufier such as sodium acetate.

Further oxidants capable of supplying acyloxy groups are acyl hypohalites, which are usually formed in situ, for example, by reaction of halogen, especially bromine or iodine, on organic carboxylic acids or of salts thereof, such as mercury-II-acylates, for example, mercury-Il-acetate (which may likewise be formed in situ, for example, from mercury-lI-oxide in the presence of glacial acetic acid) or of silver acylates, such as silver acetate, as well as by the reaction of other agents yielding positive halogen, such as N-halogenoamides or -imides, such as N-bromoacetamide, N-succinimide or N-bromohydantoin on organic carboxylic acids, such as the above-mentioned carboxylic acids, especially acetic acid.

According to the present invention the reaction may consist, for example, in treating the starting material with the appropriate quantity, that is to say at least 2 mol equivalents, of the oxidation reagent capable of furnishing acyloxy groups, conventionally in the presence of a suitable diluent, such as benzene, acetonitn'le or acetic acid, at room temperature, while cooling or preferably while heating, if necessary, in an inert gas and/or under increased pressure, the conversion into the desired acyloxy-products being carried out stepwise or directly.

Conversion in the resulting products of the acyloxy groups into the free hydroxyl groups is carried out by hydrolysis, alcoholysis, hydrazinolysis or aminolysis. Under certain circumstances the isolation of the acyloxy compound may not be necessary, as it is con verted under suitable reaction conditions directly into the desired hydroxy compound. The hydrolysis may be carried out in the absence or preferably in the presence of a basic hydrolyzing agent, such as an alkali or alkaline earth metal hydroxide, for example, sodium or potassium hydroxide, or an alkali metal or alkaline earth metal carbonate or hydrogen carbonate, for example sodium or potassium carbonate or hydrogen carbonate, or of an organic base such as pyridine or triethylamine; it may also take place when the starting material is treated with an adsorbent which is charged with water or just moist, such as a diatomaceous earth preparation (Florisil). Alcoholysis, for example by means of a lower alkanol such as methanol or ethanol, may be carried out in the presence of a transesterifying catalyst, such as a metal salt, for example alkali metal salt, such as sodium or potassium salt, or of an ammonium salt of a carboxylic acid, especially of a lower alkanecarboxylic acid, such as acetic acid, or of an arylcarboxylic acid, such as benzoic acid. Hydrazinolysis and arninolysis are achieved by treatment with hydrazine and with ammonia or a primary or secondary amine, respectively.

The above-mentioned reactions are carried out in the presence or absence of a diluent (in which case the splitting reagent, for example a lower alkanol, may also serve as solvent), if necessary while cooling or heating and/or in an inert gas and/or under superatrnospheric pressure.

It was also unexpectedly found, that, when starting with a 2,2-disubstituted L-3-acyl-5 -acyloxythiazolidine-4-carboxylic acid or a functional derivative thereof, as well as a corresponding 2,2-disubstituted L-3-acyl-5B-acyloxy-thiazolidine-4-carboxylic acid or a functional derivative thereof, or a mixture of the two isomers as the preferred starting materials, the

2,2-disubstituted L-3-acyl-5B-hydroxy-thiazolidine-4- carboxylic acids and their derivatives, respectively, are obtained almost exclusively.

In a resulting compound with a free hydroxyl group, the latter can be converted into an acyloxy group, for example, by treatment with a suitable derivative of an organic carboxylic acid, such as a halide or an anhydride thereof, or by converting the hydroxy group into a reactive esterified hydroxy group, such as a halogen, e.g. chlorine or bromine atom (for example, by treatment with a suitable acid halide, e.g. phosgene) or an organic sulfonyloxy group, e.g. methane sulfonyloxy or p-toluene sulfonyloxy group (for example, by treatment with a suitable organic sulfonic acid halide) and treatment of the resulting intermediate with an organic carboxylic acid or preferably a salt, such as an alkali metal salt thereof.

Substituents present in a resulting compound may be converted in known manner into other substituents. Thus, a resulting acid derivative, such as an ester, can be converted into the free acid without removing the acyl group, especially a readily eliminable acyl group, such as the tertiary butyloxycarbonyl group, in position 3. Thus, a earbo-lower alkoxy, such as the carbomethoxy group, can be hydrolyzed to furnish the free carboxyl group by treatment with a dilute alkali metal hydroxide, such as potassium hydroxide, solution; this conversion into the free carboxyl group may, if desired, be carried out during the splitting of the acyloxy group. Carbodiphenylmethoxy groups may be converted into free carboxyl groups under acidic conditions, for example, in the presence of catalytic amounts of an acid, such as trifluoroacetic acid. Then, a carboxyl group te ed with?tgfir al s i ser especially with 2,2,2-trichloro-ethanol, can be converted in a peculiar manner into the free carboxyl group by means of a reducing agent. Suitable reagents are chemical reducing agents, such as nascent hydrogen, obtained, for example, by the action of metals, metal alloys or amalgams upon hydrogen donors, such as zinc, zinc alloys, for example zinc copper, or zinc amalgam in the presence of acids, such as organic carboxylic acids, for example acetic acid, or of alcohols, such as lower alkanols, an alkali metal amalgam, for example, sodium or potassium amalgam or aluminum amalgam, in the presence of moist either or of lower alkanols; furthermore, alkali metals, for example, lithium, sodium or potassium, or alkaline earth metals, for example calcium, in liquid ammonia, if desired or required, with the addition of alcohols, such as a lower alkanol. Furthermore, an ester with a 2,2,2-trihalogeno-ethanol, such as 2,2,2-trichloroethanol may also be converted into the free acid by treatment with strongly reducing metal salts, such as chromium-Il-compounds, e.g. chromium- II-chloride or chromium-lI-acetate, preferably in the presence of aqueous media containing water-miscible organic solvents, such as lower alkanols, lower alkane carboxylic acids or ethers, for example, methanol, ethanol, acetic acid, tetrahydrofuran, dioxan, ethyleneglycol dimethyl ether or diethyleneglycol dimethylether.

A free carboxyl group present in a resulting compound can be converted in known manner into its functional derivatives, such as its esters, amides, hydrazides or azides. It can be esterified, for example, by treatment with a diazo compound, such as a diazo-lower alkane, for example diazomethane or diazoethane, or a phenyl-diazo-lower alkane, for example, diphenyldiazomethane, or by reaction with a hydroxy compound suitable for esterification, for example an alcohol, a phenol compound or an N-hydroxy-nitrogen compound, for example, a hydroxamic acid, in the presence of an esterifying agent, such as a carbodiimide, for example, dicyclohexyl carbodiimide, or of carbonyl diirnidazole or by any other known and suitable esterifying process, such as reaction of a salt of the acid with a reactive ester of the hydroxy compound, especially of an alcohol, and a strong inorganic acid or strong organic sulphonic acid, if desired, in the presence of a salt-forming base. Amides are prepared in known manner, sulphonylamides at the acyloxy stage, for example, by treating the free carboxylic acid with a sulphonylisocyanate.

A functionally modified carboxyl group in a resulting compound can be converted in known manner into another functionally modified carboxyl group, for example, into an esterified carboxyl group by transesterification, such as treatment with a hydroxy compound in the presence of a transesteritication catalyst. Furthennore, esters and especially activated esters, for instance, esters with N-hydroxy-nitrogen compounds, or anhydrides formed with halogenoformic acid esters, can be converted by reaction with other hydroxy compounds, such as alcohols or phenol compounds, as well as with ammonia, or with primary or secondary amines or hydrazines into other esters and amides or hydrazides, respectively. In a resulting amide or hydrazide compound with a nitrogen atom containing hydrogen, such nitrogen atom can subsequently be replaced, for example, by treatment with a reactive esterified alcohol, or, primarily in an amide or hydrazide compound of the acyloxy series, by treatment with a carboxylic or sulphonic acid derivative, such as an acid halide or by means of another suitable reagent. An N-unsubstituted amide derivative of the acyloxy series can be converted into the corresponding nitrile, for example, by dehydratation.

A resulting mixture of isomers can be resolved into the individual isomers in known manner, for example by fractional crystallization, adsorption chromatography (column or thinlayer chromatography) or by other methods. Resulting racemates can be resolved into the antipodes by forming a mixture of diastereoisomeric salts with optically active, salt-forming agents, separating the mixture into the diasteroisomeric salts and conversion of the isolated salts into the free compounds.

The compounds obtained by the present process are saturated cyclic -acyloxy-thioethers, for example, acyloxy-thiazolidines, and especially 2,2-disubstituted 3-acyl-5-acyloxy-thiazolidine-4-carboxylic acids and functional derivatives thereof, such as the compounds of the formula Va 131 -H--CH- O-Aez Aer-N S as well as saturated cyclica-hydroxy-thioesters, such as S-hydroxy-thiazolidines, and particularly 2,2-substituted 3-acyl-5-hydroxy-thiazolidine-4-carboxylic acids and functional derivatives thereof, such as the compounds of the formula Via Bi (:JHCHOH \X/ Y where Ac represents an acyl radical, especially the acyl radical of an active N-acyl derivative of cephalosporanic acid, such as the thienylacetyl, e.g. 2- thienylacetyl, chlorethylcarbamyl or phenylacetyl radical, or an easily eliminable acyl radical, such as the residue of a carbonic acid semi-ester, for example, the tertiary butyloxycarbonyl residue, AC2 represents the acyl radical of an organic carboxylic acid, such as the acyl radical of the acyloxy group supplied during the reaction, such as the acyl radical of an aliphatic carboxylic acid, for example, of an alkane carboxylic acid, such as a lower alkane carboxylic acid, primarily acetic acid or propionic acid, or of an aromatic acid, such as benzoic acid, which acids are unsubstituted or may contain further substituents, such as lower alkyl or lower alkoxy groups or halogen atoms or pseudohalogens, such as trifluoromethyl groups, X represents the disubstituted carbon atom of the 8 thiazolidine ring and R is a free or functionally modified carboxyl group.

The residue X- represents primarily the group of the formula wherein R and R each stands for a hydrocarbon residue, especially an aliphatic hydrocarbon residue, such as a lower alkyl, for example, ethyl, n-propyl, isopropyl or preferably methyl, or an aromatic group especially a phenyl group, or an araliphatic hydrocarbon residue, especially phenylalkyl, for example benzyl or phenylethyl groups, as well as functionally converted, particularly esterified carboxyl groups, such as carbo-lower alkoxy, e.g. carbomethoxy or carbethoxy groups, or R and R together may represent a bivalent hydrocarbon residue, especially bivalent aliphatic hydrocarbon residue such as a lower alkylene group, for example 1,4-butylene or 1,5-pentylene, as well as a phthaloyl group, or an 0x0 or thiono group. The abovementioned hydrocarbon residues are unsubstituted or may be substituted, for example by lower alkyl, such as methyl or ethyl, or lower alkoxy, such as methoxy or ethoxy groups, halogen such as fluorine, chlorine or bromine atoms, halogenoalkyl, such as trifluoromethyl groups, or by other suitable groups.

The group R is a free or preferably a functionally modified carboxyl group, especially an esterified carboxyl group. The latter is esterified with any hydroxy compound suitable for esterifying carboxylic acids, such as with aliphatic alcohols, for example, alkanols, particularly lower alkanols, for example, methanol, ethanol, n-propanol or tertiary butanol, or with cycloaliphatic alcohols, such as cycloalkanols, for example, cyclohexanol, or with araliphatic alcohols, such as phenylalkanols, for example benzyl alcohol or diphenylmethanol, or with phenol compounds especially phenol, or with N-hydroxy-nitrogen compounds, such as hydroxamic acids, for example, N-hydroxycarbamic acid esters, such as its methyl ester, or with N- hydroxy-imides, for example, N-hydroxysuccinimide; the above-mentioned hydroxy compounds may be unsubstituted or substituted by lower alkyl, lower alkoxy, nitro or trifluoromethyl groups or especially by halogen atoms or other groups. Substituted hydroxy compounds particularly suitable for esterifying carboxylic acids are halogenated lower alkanols, such as 2,2,2- trichlorethanol.

Other functionally modified carboxyl groups R are, for example, nitrogen-containing functionally modified carboxyl groups, such as carbamyl groups which may be unsubstituted or monoor disubstituted on the nitrogen atom by aliphatic, alicyclic, aromatic or araliphatic hydrocarbon residues or heterocyclic residues of aromatic character, which may optionally contain lower alkyl groups or free, esterified or etherified hydroxy] groups, such as lower alkoxy, aralkoxy, lower alkanoyloxy or aroyloxy groups or halogen atoms, nitro or tn'fluoromethyl groups as substituents, such residues being lower alkyl, cycloalkyl, phenyl, phenyl-lower alkyl, phenyl-lower alkylidene or pyridyl residues, or by free, etherified or esterified hydroxyl groups (such as those mentioned above), by

phosphoriferous residues or by acyl radicals, such as the radicals of carboxylic acids, for example, residues of carbonic acid semi-esters or semi-amides or lower alkanoyl residues, or of sulphonic, such as arylsulphonic acid, for example, phenylsulphonyl residues, as well as nitrile groups or azidocarbonyl groups, as well as hydrazinocarbonyl or azocarbonyl groups which may be monoor polysubstituted on the nitrogen, for example, by the above-mentioned substituents of the carbamyl group.

The present invention includes also any modification of the present process in which an intermediate obtained is used as starting material and any remaining step or steps is or are carried out with it. For example, saturated cyclic thioethers may be formed as intermediates and isolated or converted into each other, which contain in -position a hydrazono group substituted by an esterified carboxyl group, or an acyloxy group together with an azo group substituted by an esterified carboxyl group; such intermediate compounds are, for example, -hydrazono-thiazolidines or 5-acyloxy-5azo-thiazolidines, in which the hydrazono and the azo group are substituted by an esterified carboxyl group, especially 2,2-disubstituted 3-acy1-5- hydrazono-thiazolidine-4-carboxylic acids and 2,2-disubstituted 3acyl-S-acyloxy-Sazo-thiazoli-dine-4-carboxylic acids, in which the hydrazono group and the azo group, respectively, are substituted by an esterified carboxyl group, and their functional derivatives, such as the compounds of the formulas R1 NNHCOORu 5 orr-o ACi s X and 1 2. (IL-AC2 CHCN=N-COORB Ara -N in which Ac Ac R, and X have the above meanings, and R, represents the residue of an alcohol, for example, the residue of one of the alcohols mentioned above as being suitable for esterifying the carboxyl groups R especially the residue of an aliphatic alcohol, such as a lower alkanol or a substituted, preferably halogenated, lower alkanol. Such intermediates can be converted into the desired products by suitable measures either directly or stepwise. Thus, for example, a saturated cyclic thioether, which is substituted ind-position by a hydrazono group containing the esterified carboxyl group, can be converted into the desired acyloxy compound by additional treatment with an oxidation reagent capable of furnishing the acyloxy group. The desired acyloxy compound is also obtained when a saturated cyclic thioether, which contains in thea position an acyloxy group together with an azo group with the esterified carboxy substituent, is treated, for example, with a hydrolyzing agent, especially a weakly acidic or weakly basic agent, such as potassium acetate in the presence of acetic acid or sodium hydrogen carbonate in the presence of methanol, or with water, preferably on a supporting substance, such as a diatomaceous earth preparation (Plorisil). Furthermore, from a saturated cyclic thioether, which contains in thea-position an acyloxy group, together with an azo group having an esterified carboxy substituent, a saturated cyclic thioether substituted in thea-position by a hydrazono group containing the esterified carboxyl group can be for-Sled, for example, by treatment with zinc and acetic aci The invention includes also any modification in which the process is discontinued at any stage thereof, or in which starting materials are used in the form of derivatives, forexample of salts, or are formed during the reaction.

Preferred use is made of those starting materials and reaction conditions which give rise to the preferred compounds mentioned above.

The starting materials used in the above process can be prepared, for example, by the process described in US. Pat. application Ser. No. 573,816, filed Aug. 22, 1966.

The compounds obtained according to the present invention can be converted into 7-aminocephalosporanic acid and its derivatives as illustrated by the reaction scheme; this conversion may be carried out, for example, by the process described in the following U.S. Patent applications: Ser. No. 573,865, Ser. No. 573,815, Ser. No. 573,886, Ser. No. 573,866 and Ser. No. 573,876, all filed Aug. 22, 1966.

The following Examples illustrate this invention.

EXAMPLE 1 A solution of l g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-(N,N'-dicarbomethoxy-hydrazino)- thia-zolidine-4-carboxylic acid N-methyl-N- phenysulphonylamide in 50 ml of absolute benzene is treated with 1.6 g of vacuum-dried lead tetraacetate, and the mixture is stirred for 45 minutes under reflux. 0.05 ml of distilled ethyleneglycol is added, and after 10 minutes the mixture is filtered with a filter aid (Hyflo) and rinsed with benzene. The yellow filtrate is evaporated to dryness and the crystalline residue triturated with ether and pentane, cooled and filtered, to yield L-2,2-dimethyl-3-tertiary butyloxycarbonyl-S- acetyloxy-Scarbomethoxy-azo-thiazolidine-4-carboxylic acid N-methyl-N- phenylsulphonylamide of the formula 0113 HzC-Jl-O-C-N I ll on; 0 /o\ in almost colorless crystals which melt at 16l-163 C after recrystallization from methanol. Optical rotation [Q10 32 1 1 (C 1.070 in chloroform). Infrared absorption bands (in methylenechloride) at 5.69, 5.90, 6.00, 7.35, 8.10, 8.34, 8.57 and 9.24 t. Ultraviolet absorption bands (in methylene chloride) h 225;t(t= 13,000), 260p. (F 1500), 2671.1. (F 1770) and 274p. (F 1600) in ethanol, and A at about 380p. (e= about -80).

A solution of 0.663 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-S-acetoxy-5-carbomethoxyazo-thiazo1idine-4-carboxylic acid N-methyl-N-phenylsulphonylamide in 100 ml of benzene is mixed with 20 g of a diatomaceous earth preparation (Florisil) and stirred for 45 minutes at room temperature; with evolution of gas the color of the solution changes from deep yellow to light yellow to colorless. The mixture is then filtered, the residue washed with benzene and with 70 to 100 ml of ethyl acetate, and the organic solutions are evaporated. The product is chromatographed on 35 g of a diatomaceous earth preparation (Florisil). After preliminary washing with 150 ml of benzene, the crude product is eluted with 350 ml of benzene containing 1 percent of ethyl acetate. A mixture, which likewise consists predominantly of the desired product, is eluted with another 200 ml of the same solvent mixture. The crude product is recrystallized from a mixture of ether and pentane, to yield semi-crystalline to amorphous L- 2,2-dimethy1-3-tertiary butyloxycarbonyl-SB-acetylox' y-thiazolidine-4-carboxylic acid N-methyl-N- phenylsulphonylamide of the formula of which a further quantity is obtained with 100 ml of benzene containing 2 percent of ethyl acetate and with 100 ml of benzene containing 5 percent of ethyl acetate in a rather uniform state and with 50 ml of benzene containing 5 percent of ethyl acetate and 100 ml of benzene containing percent of ethylacetate as a partially crystalline mixture together with the corresponding SB-hydroxy and 5a -hydroxy compounds. After recrystallization from a mixture of methylenechloride and ether the product melts at 22022lC. Optical rotation [(11 -214 i 1 (c 0.889 in chloroform). Infrared absorption bands (in methylenechloride) at 5.75, 5.86, 5.97, 7.40, 8.25, 8.62 and 1068p.

The b2,2-dimethyl-3-tertiary butyloxycarbonyl-S- acetyloxy-S-carbomethoxyazo-thiazolidine-4-carboxylic acid-N-methyl-N-phenylsulphonylamide, which can also be converted into the desired product by treatment with a diatomaceous earth preparation (Florisil) in benzene for 17 hours at room temperature, followed by elution with ethyl acetate, is also obtained in the following manner:

A mixture of 0.02 g of L-2,2-dimethyl-tertiary butyloxycarbonyl-5-N-carbomethoxyhydrazonothiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonylamide and 1 ml of benzene is stirred for 2 hours at room temperature with a solution of 0.016 g of lead tetraacetate in 1 ml of benzene. The excess of the oxidation reagent is decomposed by adding one drop of ethyleneglycol, and the reaction mixture is diluted with benzene and washed with water. The benzene solution furnishes L-2,2-dimethyl-3-tertiary-butyloxycarbonyl-S -acetoxy-5-carbomethoxyazo-thiazolidine-4-carboxy1ic acid N-methyl-N-phenylsulphonylamide which is identified by thin-layer chromatography and its infrared spectrum.

The L-2,2-dimethyl-tertiary butyloxycarbonyl-5-N'- carbomethoxyhydrazono-thiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonylamide used above can be prepared in the following manner:

A solution of 0.193 g of crystalline L-2,2-di-methyl- 3-teitiary butyloxycarbonyl-S-acetoxy-5-carbomethoxy-azothiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonyl-amide in 10 ml of acetic acid and 0.1 m1 of water is mixed with 2 g of zinc powder and the mixture is stirred for 1 hour at room temperature, and filtered; the residue is cautiously washed with benzene, the filtrate diluted to a volume of about ml with benzene and repeatedly washed with water, the washing being washed back with benzene. The combined benzene extracts are evaporated and the residue chromatographed on 10 g of a diatomaceous earth preparation (Florisil). Benzene, benzene containing 2 percent of ethyl acetate, and 40 ml of benzene containing 5 percent ethyl acetate, elute mixtures of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxythiazolidine'4-carboxylic acid N-methyl-N-phenylsulphonamide with the corresponding fia-acetyloxy compound. A further quantity of 40 ml of benzene containing 5 percent of ethyl acetate, and 60 ml of benzene containing 10 percent of ethyl acetate, elute 2,2-dimethyl-tertiary butyloxycarbonyl-S-N-carbomethoxyhydrazonothiazolidine-4 carboxylic acid N-methyl-N-phenylsulphonylamide of the formula 11 C CH which, after crystallization from ether, melts at 163165C. Optical rotation [01],; 0 i 1 (c 1.015 in chloroform). Infrared absorption bands (in methylenechloride) at 2.99, 5.70, 5.82, 5.93 (shoulder), 6.20, 6.67, 7.40, 8.17, 8.55 and 9.351;.

EXAlvfPLE 2 A mixture of 3 ml of glacial acetic acid and 0.15 g of anhydrous sodium acetate is stirred for 35 minutes at 80C, then 0.05 g of L-2,2-d.imethyl-3-tertiary butyloxy-carbonyl--acetoxy-5-carbomethoxyazothiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonylamide is added and the whole is stirred for another 45 minutes at 80C; after 30 minutes the initially yellow mass loses its color. The reaction product is isolated by pouring the batch into water, and extraction with benzene yields the crystalline mixture of L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonylamide and the corresponding Sa-acetyl product.

Alternatively, the reaction may be carried out by treating the starting material with the triethyl ammonium acetate in hot benzene for 17 hours.

EXAMPLE 3 A solution of 0.388 g of L2,2-dimethyl-3-tertiary butyloxycarbonyl-S-acetoxy-5-carbomethoxyazothiazolidineA-carboxylic acid N-methylN-phenylsulphonylamide in ml of methylenechloride and 10 ml of methanol is mixed with 0.15 g of anhydrous sodium carbonate and then stirred for 30 minutes at room temperature. Gas is evolved and the yellow color of the solution disappears. The solution is diluted with methylenechloride, washed with water, dried and evaporated to yield a crystalline mixture of L-2,2- dimethyl-3-tertiary butyloxy-carbonyl-SB-acetyloxythiazolidine-4-carboxylic acid N-methyl-N-phenylsulphonylamide and the corresponding 5a-acetyloxy product.

EXAMPLE 4 A solution of 0.92 g of L-2,2-dirnethyl-3-tertiary butyloxycarbonyl-5B-(N,N'-dicarbethoxy-hydrazino)- thiazolidine-4-carboxylic acid methyl ester in 16 ml of acetonitrile is treated with 0.34 g of anhydrous sodium acetate and 1.4 g of lead tetraacetate free from acetic acid. The mixture is heated for 45 minutes at 60C, then evaporated under vacuum and the residue is triturated 3 times with 20 ml of hexane and with 5 ml of methylene chloride. The combined filtrates are concentrated under reduced pressure to yield a yellow oil which is again dissolved in 6 ml of acetonitrile and treated with 1.45 g of lead tetraacetate. The reaction mixture is heated for 1 hour at 60C, the lead diacetate formed is filtered off, the filtrate is evaporated and the residue is taken up in 5 ml of methylene chloride and ml of hexane. After a few minutes the extract is filtered, the filtrate once more evaporated under vacuum llnU lls

which is obtained in crystalline form when in the product obtained from the second of these three fractions the deposited crystals are freed from the oily material by being washed with pentane and then used for seeding the first and third fractions. The crystalline product is recrystallized from hexane and for analytical purposes sublimed at C under an oil pump pressure; it melts at 150-15lC. Optical rotation [01],, +203 3 2 (c 0.41 in chloroform). Infrared absorption bands (in methylenechloride) at 5.72, 5.90, 7.35, 8.23 8.55, 9.32, 9.90 and l0.35p..

A further quantity of the desired compound can be identified in the above crude product, but it is not isolated and is further worked up without previous purification.

EXAMPLE 5 2.9 Grams of lead tetraacetate are given at once into a solution of 1.265 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-(N,N'dicarbomethoxy-hydrazino)- thiazolidine-4-carboxylic acid methyl ester in 90 ml of dry benzene containing 0.3 ml of glacial acetic acid, and the mixture is refluxed. When the solid reagent has dissolved, a precipitate of lead diacetate begins to form and about 2 hours later no oxidation reagent can be detected any longer. The reaction mixture is filtered with the use of a filter aid (Celite), rinsed with benzene and the yellow filtrate is evaporated, repeatedly taken up in a mixture of benzene and heptane, and each time the solvent mixture is evaporated until the acetic acid has been completely removed.

The golden yellow, viscous-oily residue, containing L-2,2-dirnethyl-3-tertiary butyloxycarbonyl-S- acetyloxy-5-ca.rbomethoxyazo-thiazolidine-4-carboxylic acid methyl ester of the formula is chromatographed within 3 hours on 39 g of a diatomaceous earth preparation (Florisil). Elution with benzene, ether and a mixture of ether and methanol furnishes a crude product consisting predominantly of L-2,2-dimethyl-3-tertiary butyloxy-carbonyl-SB- acetyloxy-thiazolidine-4-carboxylic acid methyl ester which melts at to 148C after recrystallization from a mixture of ether, methylene chloride and hexane.

The subsequently eluted fractions and the mother liquor are combined, hydrolyzed with sodium acetate in methanol, and chromatographed on 60 times the amount of silicagel containing 5 percent of water. After washing with benzene containing 3 percent of ethyl acetate the L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid methyl ester of the formula is eluted with benzene containing 5 and 10 percent of ethyl acetate. The product can be reconverted into the L-2,2-di-methyl-3-tertiary butyloxycarbonyl-SB- acetyloxy-thiazolidine-4-carboxylic acid methyl ester by treatment with acetic anhydride for 12 hours at 100C. Optical rotation 1 +205 1 1 0.5 in chloroformhnelting at 150.5C after having been chromatographed within one hour on 50 times its weight of silica gel.

EXAMPLE 6 is eluted with benzene. Optical rotation +49 i 1 (c 1.04 in chloroform). Infrared absorption bands (in methylenechloride) at 5.74, 5.90 and 8.25pm.

EXAMPLE 7 A solution of 0.14 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4-carboxylic acid 2,2,2-trichloroethyl ester in 3.5 ml of 90 percent acetic acid is mixed with 1.5 g of zinc dust, and the reaction mixture is stirred for 4 hours at room temperature. The batch is filtered and the residue rinsed with 4 ml of acetic acid and 200 ml of benzene; the filtrate is washed 5 times with water, dried over magnesium sulphate and evaporated. The residue crystallizes on being triturated with a mixture of pentane and ether and is recrystallized from a mixture of ether and hexane. The resulting L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetoxy-thiazolidine-4-carboxylic acid of the formula melts at 145-l46C after having been subiimed at 127C under a pressure of 0.001 mm Hg. Optical rotation [(11 +225 (c 0.93 in chloroform). infrared absorption bands (in methylenechloride) at 5.75, 5.90 and 8.25

EXAMPLE 8 A solution of 25.23 g of 1:2,2-dimethyl-3-tertiary butyloxycarbonyl-5fl-(N,N-dicarbomethoxyhydrazino )-thiazolidine-4-carboxylic acid 2,2,2- trichloroethyl ester in 300 ml of benzene is mixed with 49 g of lead tetraacetate and the mixture is kept for 45 minutes at a gentle boil. After cooling and filtering the filtrate is evaporated in a water-jet vacuum and the residue chromatographed on 750 g of a diatomaceous earth preparation (Florisil). The crude mixture of L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-Sa-acetyloxy-thia-zolidine-4-carboxylic acid 2,2,2-trichloroethyl ester and its SB-acetoxy isomer is eluted with 2,500 ml of a 98:2-mixture of benzene and ethyl acetate. On crystallization from pentane there is obtained the L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4-carboxylic acid 2,2,2-tri-chloroethyl ester melting at 87C.

The mother liquor furnishes the non-crystallizing L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-Sa -acety]oxy-thia-zolidine-4-carboxylic acid 2,2,2-trichloroethyl ester of the formula 000011810013 221. /ou -cn--o-co-om mc -co c-N s I II on. o o

EXAMPLE9 A mixture of 1 1.82 g of L-2,2-dirnethyl-3-tertiary butyloxycarbonyl-5B-( N,N '-dicarbomethoxy-hydrazino thiazolidine-4-carboxyiic acid 2,2,2-trichloroethyl ester in 150 ml of benzene and 24.4 g of lead tetraacetate is heated for 45 minutes at a gentle boil, cooled, filtered and evaporated under vacuum. The yellow, oily residue contains the L-2,2-dimethyl-3-te rtiary butyloxycarbonyl-S-acetyloxy-5-carbomethoxyazothiazolidinei carboxylic acid 2,2,2-trichloroethyl ester; it is taken up in 200 ml of warm hexane, filtered, and the filtrate is evaporated. The residue is dissolved in 250 ml of benzene, mixed with 100 g of a diatomaceous earth preparation (Florisil) and 5 ml of ethyl acetate and stirred for minutes. The batch is filtered and the filtrate evaporated, to yield a crude mixture of L-2,2-dimethyl-3-tertiary-butyloxycarbonyi- 5a-acetyloxy-thiazolidine-4 carboxylic acid 2,2,2- trichloroethyl ester and its SB-acetyloxy isomer.

EXANIPLE 10 A solution of the mixture obtained by the process described in Example 9 in 200 ml of glacial acetic acid and 20 ml of water is mixed with 60 g of zinc dust and stirred for 3 hours at room temperature. The mixture is then filtered and the filter residue washed with 60 ml each of glacial acetic acid and benzene. The filtrate is evaporated under 0.5 mm Hg, the residue taken up in 600 ml of ether and the solution washed with 600 ml of water, and the aqueous phase is rinsed with ether. The combined ether solutions are twice washed with water, dried and evaporated, and the residue dissolved in ether, treated with an active carbon preparation and crystallized from a mixture of ether and pentane, to

m.p. l7l17l.5C; [04],, =*346 i 1 (c 0.925 in chloroform); infrared absorption spectrum (in methylenechloride) with bands at 2.87, 3.15, 5.75, 5.90, 5.96, 7.25, 7.35, 8.25, 8.63 and 10.66;.L; together with a major quantity of a crystalline mixture of the two acids.

EXAMPLE 11 A mixture of 0.25 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-(N,N'-dicarbethoxy-hydrazino)- thiazolidine-4-carboxylic acid N-acetylamide in ml of boiling benzene is treated with 0.45 g of lead tetraacetate and refluxed for 60 minutes. The reaction mixture is then concentrated under a water-jet vacuum to about 5 ml, diluted with 25 ml of hexane and filtered. The filtrate is concentrated under vacuum and the yellow oily residue chromatographed on silica gel. The L- 2,2-dimethyl-3-tertiary butyloxy-carbonyl-Sacetyl-S- carbethoxyazo-thiazolidine-4-carboxylic acid N- acetylamide of the formula H3CC ONH-( 3O oo o orn on; /C IIC-N=NC o 0 02115 I rho-c-o-c-n s l H o m o 1130 C IL;

is eluted with a 9zl-mixture of benzene and ethyl acetate, Treatment of the eluate with a diatomaceous earth preparation (Plorisil) furnishes a mixture of L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4-carboxylic acid N-acetylamide of the formula and its 5a-acetyloxy isomer.

EXAMPLE 12 A solution of 0.831 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxythiazolidine-4-carboxylic acid in 10 ml of methylenechloride is mixed with 0.36 ml of triethylamine, cooled to l0C and treated with 0.25 ml of Cl'llOIOfOI'HllC acid ethyl ester in 4 ml of cold methylene chloride. The reaction mixture is kept for minutes at 1 0 to 5C under anhydrous conditions and then treated for 3 hours with a strong current of dry gaseous ammonia. The batch is kept for 10 minutes at 0C and for 40 minutes at room temperature and then filtered, the filter residue rinsed with methylenechloride and the filtrate evaporated. The residue is dissolved in 30 ml of methylene chloride, and the solution is agitated with 5 g of silica gel containing 5 percent of water and filtered. The silica gel is rinsed with 9:1-mixtures and 5:1-mixtures of methylene chloride and alkyl acetate, to yield L-2,2-dimethyl- 3- tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4- carboxylic acid amide of the formula as a colorless glass which can be distilled at l 30C under 0.001 mm Hg pressure as a viscid, colorless oil. Infrared absorption bands (in methylenechloride) at 2.86, 2.96, 5.75, 5.92, 6.38, 7.25, 8.25, 7.42, 8.25, 8.65, 9.2, 9.35, 9.88 and 10.40 ;1..

EXAMPLE 13 980 Grams of lead tetraacetate are tipped into a solution of 384 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5-( N,N-dicarbomethoxy-hydrazino)- thiazolidine-4-carboxylic acid methyl ester. The solution turns dark brown and is heated, whereupon it becomes golden yellow and white lead diacetate begins to separate. The batch is stirred for 2 hours under reflux and 0.5 ml of ethyleneglycol is added; the reaction mixture is filtered through a glass filter and the residue washed with a total of 4,000 to 5,000 ml of dry benzene. The combined filtrates are evaporated under vacuum and the yellow, oily residue is taken up in 3 X 500 ml of dry benzene and the solvent is evaporated under vacuum each time. The slowly crystallizing residue is taken up in methylene chloride, the solution filtered and evaporated. The reaction product, consisting predominantly of a mixture of L-2,2-di-methyl-3- tertiary butyloxycarbonyl-Sa-acetyloxy-thiazolidine-4- carboxylic acid methyl ester and its SB-acetyloxy isomer, as well as of 2,2-dimethyl-3-tertiary butyloxycarbonyl-4-thiazoline-4-carboxylic acid methyl ester and L-2,2-dimethyl-3-tertiary butyloxycarbonyl-S- acetyloxy-Scarbomethoxyazo-thiazolidine4-carboxylic acid methyl ester, is further processed without further purification.

A solution of 363 g of the product in 8,000 ml of dry methanol is mixed with g of sodium acetate and the mixture is refluxed with stirring for 24 hours and then cautiously evaporated under vacuum. The residue is stirred with 2 X 1500 ml of benzene and each time evaporated to dryness, and then thoroughly extracted within 6 hours with a total volume of 5,000 ml of methylene chloride. The organic soluu'on is evaporated and the resulting dark brown oil dissolved in 1,000 ml of dry benzene and chromatographed on 1,900 g of silica gel containing percent of water, in each case collecting fractions of 2,000 ml. 16,000 to 18,000 ml of benzene, containing 3 percent of ethyl acetate elute in the first place apolar by-products; subsequent elution with 40,000 ml of benzene containing 5 percent of ethyl acetate and 8,000 ml of benzene containing percent of ethyl acetate furnishes the L-2,2-dirnethyl-3- tertiary butyloxycarbonyl-5fl-hydroxy-thiazolidine-4- carboxylic acid methyl ester of the formula in the form of a yellow oil which crystallizes from hexane containing a trace of ether as an almost white product melting at 10l-102C (after drying for 3 hours at 90C under 0.01 mm Hg pressure). Optical rotation [a =+48 1 (c= 1.14 in chloroform). Infrared absorption bands (in methylenechloride) at 2.80, 5.75, 5.95, 7.35, 8.65 and 935p; end absorption in the ultraviolet spectrum (in 95 percent methanol). The resulting mother liquor is once more chromatographed on silica gel to yield a further amount of the desired product.

Eluted as polar by-product are in the first place the 2,2-dimethyl-3-tertiary butyloxycarbonyl-4-tl'iiazoline- 4-carboxylic acid methyl ester boiling at 65C under 0.001 mm Hg pressure and melting at 3436.5C; infrared absorption bands (in methylene chloride) at 5.88, 6.37, 7.34, 7.45, 7.62, 8.24, 8.65, 8.85, 9.32 and 1 1.91,u.', ultraviolet absorption bands (in ethanol) A 270 my. (e 5320) and 316 my. (e= 5960), and the L- 2,2-dimethyl-3-tertiary butyloxycarbonyl-4-hydroxythiazolidine-S-one-4-carboxylic acid methyl ester melting at l13.5-114C. Optical rotation [041 -1 1 1 (in chloroform). Infrared absorption bands (in methylenechloride) at 2.85, 5.70, 5.85, 7.60, 8.95, 10.25 and 10.45p.. Ultraviolet absorption bands (in 96 percent ethanol) A,, 237 mu (e=4350).

EXAMPLE 14 A solution of 0.084 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-Sa -acetyloxy-thiazolidine-4-carboxylic acid in 0.56 ml of 1N sodium hydroxide solution is kept for. 2 hours at room temperature, then mixed with 0.13 g of citric acid and repeatedly extracted with methylenechloride. The organic extracts are evaporated to yield L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-hydroxy-thiazolidine-4-carboxylic acid of the formula coon cuon-o n which melts at C on recrystallization from a mixture of ether and pentane. Optical rotation {(219 +l27 1 1 (c 0.8 in 1N sodium hydroxide solution). infrared absorption bands (in potassium bromide) at 2.82, 5.75, 6.02, 7.25, 8.02, 8.40, 8.65, 9.20, 9.70, 10.89, 11.65, 12.90 and l3.30p..

EXAMPLE 15 A solution of 2.05 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-acetyloxy-thiazolidine-4-carboxylic acid in 13 m1 of 1N sodium hydroxide solution is kept for 2 Mt hours at room temperature, then mixed with 2 g of citric acid and repeatedly extracted with methylene chloride. The dried organic extracts are evaporated and the residue crystallized from a mixture of acetone and hexane, to yield L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid of the formula melting at 185C. Optical rotation {011 +123 i 1 (c 1 in IN sodium hydroxide solution).

EXAMPLE 16 0.035 Gram of L-2,2-dimethy1-3-tertiary butyloxycarbonyl-5,B-hydroxy-thiazolidine-4-carboxylic acid in 2 ml of ether is treated with an ether solution of diazornethane, and the crude product is dissolved in a 9:1-mixture of benzene and ethyl acetate and filtered through 1.2 g of silica gel, to yield pure L-2,2-dimethyl- 3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4- carboxylic acid methyl ester which is identical with the product obtained by the process of Example 13.

EXAMPLE 17 comp out 0HCHOH HsC( )0C-N s OH; (I)

o IsC \C Ha whose infrared spectrum (in methylene chloride) contains bands at 2.80, 2.87, 2.95, 5.95, 6.40, 7.25, 7.35, 7.45, 8.65, 9.20, 9.35, 9.83 and 1166p.

, 21 EXAMPLE 18 A mixture of 6.24 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl--(N,N'-dicarbomethoxy-hydrazino)- thiazolidine-4-carboxylic acid 2,2,2-trichloroethyl ester and 60 ml of benzene is treated with 10.33 g of lead tetraacetate and refluxed for 30 minutes. After cooling and filtering, the filtrate is evaporated under vacuum, to yield a yellow, oily residue consisting predominantly of a mixture of L-2,2-dimethy1-3-tertiary butyloxycarbonyl-S -acetyloxy-thiazolidine-4- carbo-xylic acid 2,2,2-trich1oroethyl ester and its 55- acetyloxy isomer, as well as the L-2,2-dimethyl-3-tertiary butyloxycarbonyl-S-acetyloxy-S-carbomethoxyazothiazolidine-4-carboxylic acid 2,2,2-tn'chloroethyl ester; this mixture is further worked up without being further purified.

By chromatography of the resulting product mixture on 180 g of a diatomaceous earth preparation (Florisil) and elution with 1000 ml of a 98:2-mixture of benzene and ethyl acetate there is obtained as the main product L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetoxy-thiazolidine-4-carboxylic acid 2,2,2-trichloroethyl ester, whereas subsequent fractions eluted with the same solvent mixture furnish L-2,2-dimethyl-3-tertiary butyloxycarbonyl-S[3-hydroxy-thiazolidine-4-carboxylic acid 2,2,2-trichloroethyl ester of the formula as a colorless oil boiling at 115C under 0.005 mm Hg pressure. Infrared absorption bands (in methylene chloride) at 2.75, 5.65, 5.72, 5.85, 5.90, 7.35, 8.60, 9.16, 9.32, 9.78 and 11.6,u..

EXAMPLE 19 A solution of 0.274 g of crude L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-acetyloxy-thiazolidine-4- carboxylic acid N-methyl-N-phenylsulphony1amide in 3 ml of dimethylformamide is mixed with 0.05 ml of anhydrous hydrazine and the mixture is stirred for 5 hours at room temperature, then poured into 30 ml of saturated sodium chloride solution and extracted three times with 90 ml of methylene chloride in 3 portions. The organic extract is once washed with saturated sodium chloride solution and evaporated. The crude product is dissolved in 40 ml of methylene chloride and washed with 2 X 30 ml of percent aqueous citric acid solution and once with 30 ml of water. The acid extracts are adjusted with aqueous ammonia to pH about 9 and extracted with 3 X 40 m1 of methylene chloride. The organic extracts are evaporated and the crystalline residue is recrystallized from a mixture of ether and pentane, to yield L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid hydrazine of the formula where after recrystallization melts at 154-155C. Optical rotation [11] +16 1- l (c 1.119 in chloroform). Infrared absorption bands (in methylene chloride) at 2.78, 2.92, 3.03, 6.00, 6.19, 7.25, 7.36,

7.50 and 8.14 4.

EXAMPLE 20 melting at 177 to 181C. Infrared absorption bands (in methylene chloride) at 2.80, 2.99, 3.44, 5.90, 5.98, 7.42, 8.30, 8.62, 9.20, 9.38, 9.82, 9.94 and 10.7811.

EXAMPLE 21 A solution of 0.322 g of diphenyldiazomethane in 5 ml ether is added dropwise over a period of 10 minutes and while stirring to a solution of 0.456 g of L-2,2- dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxythiazolidin-4-carboxylic acid in 7 ml of ether. The reaction mixture is allowed to stand over night, then filtered and the filtrate is evaporated under reduced pressure. The resulting yellowish syrup is chromatographed on 39 g of silica gel; the column is prepared with benzene and 50 rrrl fractions are taken, a 19:1-rnixture of benzene and ethyl acetate being used for the elution. Fractions 4-8 are evaporated and combined and the product dried over night at 50C/0.0l mm Hg to yield the glass-like yellowish L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid diphenylmethylester of the formula which in the infrared spectrum (in methylene chloride) shows bands at 2.75, 3.45, 5.72, 5.90 and 7.35

EXAMPLE 22 A solution of 0.104 g of L-2,2-dimethyl-3-tertiary butyloxycarbonyl-3-tertiary butyloxycarbonyl-Sflacetyloxy-thiazolidin-4-carboxylic acid-N-phenylsulfonyl-amide in 2 ml of dioxan is diluted with 2 m1 of water, cooled with ice and, while stirring, quickly treated with 4.54 ml of an 0.1N sodium hydroxide solution. The solution is stirred at C during minutes, diluted with 50 ml of methylene chloride and washed with 10 ml of a 10 percent aqueous citric acid solution and with 50 ml of water,dried and evaporated. The residue is crystallized from a mixture of ether and pentane to yield the L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5,6-hydroxy-tl'iiazolidin-4-carboxylic acid-N- phenylsulfonylamide of the formula which melts at 164-l65C after recrystallization from methylene chloride and hexane; [a L -26 i 1 (c 1.62 in chloroform); infrared absorption spectrum (in methylene chloride) with bands at 2.75, 3.00, 5.85 and 6.07 pr.

The starting material is prepared by reacting L-2,2- dimethyl-3-tertiary butyloxycarbonyl-5B-acetyloxythiazolidine-4-carboxylic acid (Example 7) with phenyl sulfonylisocyanate in the presence of triethylamine and dry benzene as the solvent. The L-2,2-dimethyl-3- tertiary butyloxycarbonyLS/i-acetyloxy-thiazolidine-4- carboxylic acid-N-phenylsulfonylamide of the formula melts at l50l52C after recrystallization from a mixture of methylenechloride, ether and pentane; +57 1 1 (0 1.032 in chloroform); infrared absorption spectrum (in methylene chloride) with bands at 3.0, 5.73, 5.83, 5.95, 6.07, 7.06, 7.25, 7.34, 8.20, 8.43, 8.50, 9.20, 9.85 and 10.36 ultraviolet absorption spectrum (in ethanol) with A at 223 my. (e= 23,000), 260 my. (6 810), 267 my. (6 1100) and 273 mp. (e= 920).

EXAMPLE 23 A solution of 5 g of L-2,2-dimethyl-3tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-l-carboxylic acid methyl ester in 150 ml of a lzl-mixture of tetrahydrofuran and methanol is cooled to -l 5C and slowly treated with 30 ml of a 0.5N aqueous sodium hydroxide solution; the addition takes about 1 hour. After acidifying the reaction mixture with 2 ml of acetic acid (pH about 6) and evaporating it under reduced pressure to a volume of about 50 ml; a total of 200 ml of water is slowly added while stirring. As soon as an oily precipitate is formed, the reaction mixture is seeded with a small amount of L-2,2-dirnethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid methyl ester and cooled, while continuing the addition of the water. After stirring for 1 hour at 0, the mixture is filtered; the solid material is dried over calcium chloride under reduced pressure and at room temperature. The resulting crude L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5B-hydroxy-thiazolidine-4-carboxylic acid methyl ester melts at 9899 and may be used without further purification. By extracting the filtrate twice with 100 ml of methylene chloride one obtains a further amount of the desired hydroxy ester in crude form.

It can also be purified as follows: A mixture of 21.4 g of the crude L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4-carboxylic acid methyl ester and ml of ether is concentrated to 80 ml, diluted with ml of hexane and concentrated under normal pressure to 100 ml. After seeding the temperature is slowly brought to room temperature and the mixture is allowed to stand at -l0 over night. The precipitate is filtered off to yield the L-2,2-dimethyl-3- tertiary butyloxycarbonyl-SB-hydroxy-thiazolidine-4- carboxylic acid methyl ester melting at 100] 03.

EXAMPLE 24 A solution of 1.145 g of L-2,2-dirnethyl-3-tertiary butyloxycarbonyl-5fi-hydroxy-thiazolidine-4-carboxylic acid methyl ester in 30 ml of ethanol-free methylene chloride is treated with 30 ml of triethylamine and then during 2 minutes with phosgene. The mixture starts to boil and triethylammonium chloride precipitates; it is immediately concentrated under reduced pressure to about 5 g to a half-crystalline residue which is extracted several times with warm ether. After filtering, the organic solvent is concentrated under water pump vacuum and the oily residue, containing the L-2,2- dimethyl-B-tertiary butyloxycarbonyl-S-chlorothiazolidine-4-carboxylic acid methyl ester of the formula is dissolved without further purification in 20 ml of acetic acid and stirred with 2 g of sodium acetate. The clear solution is becoming turbid (precipitation of sodium chloride) and after 2 hours, the dispersion is evaporated under reduced pressure; at the end a small amount of toluene is added, and also evaporated. The residue is taken up in 50 ml of water and 50 ml of methylene chloride, the organic phase is washed twice with 50 ml of water, dried and evaporated under reduced pressure. The oily residue crystallizes and is taken up in 5 ml of a lzl-mixture of hexane and pentane. The crystalline product is filtered off and represents the L-2,2-dimethyl-3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine-4-carboxylic acid methyl ester, which melts at l45-l48 after washing with pentane.

The hexane-pentane-solution is evaporated and the oily residue is chromatographed on 50 g of silica gel, the column being prepared with benzene:

Fraction solvent ml weight g) l benzene 100 0.001 benzene con- 100 0.001

taining 5 EXAMPLE 26 ethyl acetate 2 120 8 2 A solution of 0.773 g of the crystalline L-2,2- 52 l 39 2: dirneth yl-3-tertiary-butyloxycarbonyl-SB-acetyloxy- 6 50 09-12(03) 5 tluazohd1ne-4-carboxyl1c acid 2,2,2-trichloroethylester 2g 3%: in 12 ml of methanol is cooled to l0 and treated over a period of 2 minutes with 1.72 ml of a 1N aqueous sodium hydroxide solution. After stirring for 18 Fracnons are taken together and mulled; the minutes, the reaction mixtureispoured into ice-cooled desired f 10 2N aqueous citric acid and the mixture is extracted 5a'acetyloxyfluamhdme4'carboxyhc acld methyl with methylene chloride. The colorless oil obtained ester of the formula after evaporating the organic solution is chromatogr; o 0 all, raphed on 10 g of silica gel containing 5 percent water.

A small amount of 2,Z-dimethyl-3-tertiary-butyloxycarnn /CIIC------O%CH3 bonyl-4-thiazoline-4-carboxylic acid 2,2,2- lnc-c-o-c-N s 0 trichloroethylester is eluted with benzene; with (3'13 methylenechloride the main fraction, i.e. the L-2,2-

dirnethyl-3-tertiary-butyloxycarbonyl-SB-hydroxythiazolidine-4carboxylic acid 2,2,2-trichloroethylester v is washed out, whereas the transesterification product, is obtained in 100 0.001 mm Hg; [01],, -331 1 i.e. the L-2,Z-dimethyl-3-tertiary-butyloxycarbonyl-5B- 0,88 i hl f i fi d b ti Spectrum hydroxy-thiazolidine-4-carboxylic acid methylester is (in methylene chloride) at 5.72, 5.87, 7.35, 8.20, 8.60, eluted with methylenechloride containing 10 percent 9.30, 9.85 and 1065 1., the last band being particularly of methanol- The b2,2-dimefl1yl-3-tertiary s/ strong and absent in the spectrum of the corresponding Y Y B "hydfoxy-flliazolidine'4'cal'boxylic acid L-2 ,2-dimethyl-3-tertiary butyloxycarbonyl-SB- 9 y crystallizes from a Concenacetyloxy-thiazolidinei-carboxylic acid methyl ester. Hated m and melts at 1040-1050- When treated with sodium acetate in methanol ac- 161mm: cording to the procedure illustrated by example 13, the A process for the Preparauon of compounds of the product yields in good yield the L-2,2-dimethyl-3-tertifmmfla ary butyloxycarbonyl-5B-acetyloxy-thia2lolidine-4-carboxylic acid methyl ester. R1

EXAMPLE 25 cn on Mono A solution of 20 g of the crystalline L-2,2-dimethyl- 3-tertiary butyloxycarbonyl-SB-acetyloxy-thiazolidine- X 4-carboxylic acid methyl ester and 8 g of anhydrous sodium acetate in 400 ml of anhydrous methanol is 40 Stirred at room p ur under exclusion of wherein Ac is the acyl residue of a semiester of carture. Stirring is discontinued, as soon as a clear solution bonic acid, X stands for the group of the formula is obtained; the latter is allowed to stand at room temperature for 10 days and is then concentrated to a volume of about 100 ml and, while cooling with ice, 5

slowly treated with 400 ml of water. As soon as an oily precipitate is formed, the mixture is seeded with a small amount of L-2,2-dimethyl-3-tertiary butyloxycarbonyl- 5B-hydroxy-thiazolidine-4-carboxylic acid methyl ester; after completion of the water addition the reaceach of the groups 2 and s is lower alkyl tion mixture is stirred at 0 for another 30 minutes, then havmg one to three cal'bon atoms, 1 represents a filtemd and the residue washed with water and dried member selected from the group consisting of a free for 3 days over calcium chloride at 15 mm pressure. carboxyl group a carboxyl group F f by a The resulting L 22 dimethyl 3 teniary butyloxycap member selected from the groups conslstlng of a lower bonyl-SB-hydroxy-thiazolidine-4-carboxylic acid haloilower alkanol or a phenyHower methyl ester melts at 0 e anol, each having up to four carbon atoms in the al- From the aqueous extracts a further amount of the f ai carbamyl q a mmle group an crude hydroxy-ester can be obtained by extraction with if; Clear ny x gs i and an azocar' methylene chloride; the crude material can be purified k gfi C2 is g residue of a lower as follows: 4.8 g of the crude L-2,2-dimethyl-3-tertiary fi g ig g g gl fig ii g fi whlch butyloxycarbonyl-5,B-hydroxy-thiazolidine-4-carboxylp g p e cm a ic acid methyl ester in 120 ml of hexane is filtered through a column of 24 g of silica gel containing 5 perf 000R cent of water. After washing with 180 ml of hexane, the CPI-H 0 column is eluted with 200 ml of a benzene-ethyl acetate l mixture; the resulting product melts at 94-98.

in which Ac X and R are defined as above and R and R are each residues of a member selected from the group consisting of a lower alkanol and a halogenated lower alkanol, each having up to four carbon atoms, with an oxidizing agent selected from the group consisting of a heavy metal acylate, an acyl hypohalite, and an N-halogenoamide or an N-halogeno-imide in the presence of a carboxylic acid, the acyl residue in each of said oxidin'ng agents being derived from a member selected from the group consisting of an aliphatic or aromatic carboxylic acid.

2. A process as claimed in claim 1, wherein lead tetraacetate is used.

3. A process as claimed in claim 1, wherein the oxidizing reagent yielding an acyloxy group is a member selected form the group consisting of thallium-III acylates and mercury-II acylates.

4. A process as claimed in claim 1 wherein at least 2 mol equivalents of the oxidizing agent yielding acyloxy groups are used.

5. A compound of the formula as! Ta .7

in which each of the groups R and R is lower alkyl having one to three carbon atoms, R represents a member selected from the group consisting of carboxyl, carboxyl esterified by lower alkanol, carboxyl esterified by halogeno-lower alkanol or carboxyl esterified by phenyl-lower alkanol, the aliphatic portion of each of said lower alkanol moieties having up to four carbon atoms, and Ac; is the acyl radical of a lower alkanoic acid having two to three carbon atoms.

6. A compound as claimed in claim 6 and having the formula CH- C H M 0 A02 Aer-N in which Ac, is an easily eliminable acyl residue of a semi-ester of carbonic acid, R is a member selected from the group consisting of carboxyl, carboxyl esterified by lower alkanol and carboxyl esterified by halogenated lower alkanol, the aliphatic portion of each of said lower alkanol moieties having up to four carbon atoms, and A0 is the acyl radical of lower al- 

2. A process as claimed in claim 1, wherein lead tetraacetate is used.
 3. A process as claimed in claim 1, wherein the oxidizing reagent yielding an acyloxy group is a member selected form the group consisting of thallium-III acylates and mercury-II acylates.
 4. A process as claimed in claim 1 wherein at least 2 mol equivalents of the oxidizing agent yielding acyloxy groups are used.
 5. A compound of the formula wherein Ac1 is an easily eliminable acyl radical of a semiester of carbonic acid, X stands for the group of the formula in which each of the groups R2 and R3 is lower alkyl having one to three carbon atoms, R1 represents a member selected from the group consisting of carboxyl, carboxyl esterified by lower alkanol, carboxyl esterified by halogeno-lower alkanol or carboxyl esterified by phenyl-lower alkanol, the aliphatic portion of each of said lower alkanol moieties having up to four carbon atoms, and Ac2 is the acyl radical of a lower alkanoic acid having two to three carbon atoms.
 6. A compound as claimed in claim 6 and having the formula in which Ac1 is an easily eliminable acyl residue of a semi-ester of carbonic acid, R1 is a member selected from the group consisting of carboxyl, carboxyl esterified by lower alkanol and carboxyl esterified by halogenated lower alkanol, the aliphatic portion of each of said lower alkanol moieties having up to four carbon atoms, and Ac2 is the acyl radical of lower alkanoic acid having two to three carbon atoms.
 7. A compound as claimed in claim 5 and being L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5 Beta -acetyloxy-thiazolidine-4-carboxylic acid methyl ester.
 8. A compound as claimed in claim 5 and being L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5 Alpha -acetyloxy-thiazolidine-4-carboxylic acid methyl ester.
 9. A compound as claimed in claim 5 and being L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5 Beta -acetyloxy-thiazolidine-4-carboxylic acid 2,2,2-trichloro-ethyl ester.
 10. A compound as claimed in claim 5 and being L-2,2-dimethyl-3-tertiary butyloxycarbonyl-5 Alpha -acetyloxy-thiazolidine-4-carboxylic acid 2,2,2-trichloro-ethyl ester. 